The present invention relates to a process for producing a carbon product of coarse and dense structure and, more particularly, to such a process for producing a carbon product having a coarse and dense structure in which coarse structure carbon moldings and dense structure carbon moldings are alternately constructed.
In this specification, carbon refers to both carbonaceous material and graphite, coarse structure means a structure made of porous carbon, and dense structure means a structure of carbon material which is formed by: (1) adding a binder and, as required, a filler, (2) precarbonizing the mixture, then (3) carbonizing it in an inert gas atmosphere. The structure of ultrafine crack at the binder section which is typically formed in the carbonizing step is not referred to as a porous structure. The moldings produced by mixing and kneading a mixed structure to obtain a dense structure, then shaping the mixture into an arbitrary shape by a molding machine is called "a green molding". Further, a carbonized material is produced by insolubilizing or infusibilizing the green molding by, for example, adding a carbonization accelerating catalyst, a crosslinking agent or a polymerization starter oxidizing, heating and crosslinking at 50.degree. to 300.degree. C. in an atmosphere of Cl.sub.2, O.sub.3, or air, or crosslinking and curing by emitting ultraviolet rays, an electron beam, or other radiation beam.
A carbon product has excellent oxidation resistance and medicine resistance, is not fusibly deformed in a nonoxidative atmosphere but exhibits excellent heat resistance and corrosion resistance. A porous material which is formed of carbon having such excellent properties may be utilized for various types of filters for isolating solid in liquid, as a catalytic carrier, as activated charcoal or adsorber by imparting or treating with a medicine, or for a light-weight structure, a heat insulator, electrodes for a battery, or a panel heater. Dense structure carbon moldings may be used for a heat exchanger distillation unit, an evaporator, an adsorber, a condenser, or a filter.
For producing a porous carbon, there exists a process comprising calcining a resin foam such as phenol or urethane. According to this process, the carbonization rate of resin is generally low, and the process has a drawback in that the formation of a starting material causes a large volumetric shrinkage due to the carbonization, thereby reducing the strength. As an improved process for eliminating the above-described drawbacks, a process for producing a porous carbon by carbonizing a mixture produced by impregnating resin foam such as phenol foam or urethane foam with resin such as epoxy or furan resin has been proposed. Further, a process has been disclosed for producing a carbon by mixing an amorphous or spherical carbon or graphite with resin, tar or pitches, molding the mixture and then carbonizing it (disclosed in Japanese Patent Application Laid-open No. 67,188/1973). However, the porous carbon produced by this process has relatively small porosity (L00 -L30) with relatively large apparent gravity. In addition, a process for producing a carbon by molding ultrafine carbonaceous hollow material and then carbonizing the material has also been proposed (Japanese Patent Publication No. 19,999/1974). According to this process, the carbon has relatively small apparent gravity (0.05 to 1.00) and most of the pores are independent, thereby providing extremely low ventilation. Further, there has been proposed a process for producing a porous carbon by introducing inflammable gas to thermosetting resin foam obtained by reacting directly the mixture with polyisocyanate and phenol resin or furan resin of its precarbonized material, breaking cell membranes by igniting the gas, and then carbonizing the material to provide continuous pores (Japanese Patent Application Laid-open No. 125,289/1978). Moreover, a process for producing a porous carbon by mixing an inorganic material or a carbonizable organic material, polyvinyl alcohol, aldehydes as a crosslinking agent and water soluble salts, solidifying the mixture, then solubilizing water soluble materials in water to form continuous pores and carbonizing the material has also been proposed (Japanese Patent Application Laid-open No. 51,109/1982). However, this method is disadvantageously complicated.